Mixed brand MCBs and EICR coding

[stillp]

it was this thread //www.diynot.com/diy/threads/zig-zag-unsafe-zone.446013/page-5#post-3503830

 

[JohnW2]

An absence of historical accident data is not to be taken as an indication of an absence of risk.

We've already agreed about that, but it's equally true that in the absence of any 'accident data' one cannot take theoretical arguments as necessarily indicating that there is a risk of adequate magnitude to warrant/justify any action. The same is even true if there is only a very small amount of 'accident data'.

Kind Regards, John

 

[stillp]

We'll have to agree to differ then, since that is exactly what HSE and BIS would expect in the industrial sector.

 

[JohnW2]

We'll have to agree to differ then, since that is exactly what HSE and BIS would expect in the industrial sector.

Interesting. As I said, such a view would logically lead to attempts to find ways of reducing even those risks which, although theoretically possible (very little is 'impossible!), were of 'vanishingly small' probability.

Kind Regards, John

 

[EFLImpudence]

So, if the brake pads for a Smart happen to be the same size as those for a Bugatti Veyron, and both vehicles have passed their type tests, you would expect those brake pads to be interchangeable?

That's obviously unlikely to be the case but IF they were and they had then they would be, wouldn't they?

 

[ban-all-sheds]

What if they are interchangeable by virtue of physical dimensions but made of different materials because of the large differences in mass and potential speeds of the two vehicles?

 

[JohnW2]

Much as it may seem odd that I should be 'siding' with stillp, I think that EFLI has chosen to cite just about the worst two possible automotive analogies! In the case of both tyres and brake pads, satisfactory/safe normal performance of the vehicle to which they are fitted is dependent on a set of four of the items concerned. If, per EFLI's suggestion, one of the four is different in that it exceeds the requirements of the product Standard by much more than the other three, then it is quite possible that the 'set of four' would not function satisfactorily/safely, even though all four satisfied the product Standard.

This is a pretty unusual situation. Certainly in the context we are discussing, the performance of an MCB in normal operation is in no way dependent on the nature/performance any other devices.

Kind Regards, John

 

[stillp]

We'll have to agree to differ then, since that is exactly what HSE and BIS would expect in the industrial sector.

Interesting. As I said, such a view would logically lead to attempts to find ways of reducing even those risks which, although theoretically possible (very little is 'impossible!), were of 'vanishingly small' probability.

Yes, that's what I've been trying to tell you.

Much as it may seem odd that I should be 'siding' with stillp

Stranger things have happened!

Certainly in the context we are discussing, the performance of an MCB in normal operation is in no way dependent on the nature/performance any other devices.

That is wrong, and an irresponsible post to make on a public forum.

 

[EFLImpudence]

I appreciate the differences mentioned but in my original point I only referred to the speed rating of the tyre, obviously all the other criteria would have to be the same.

Is that not analogous to MCBs which have all passed the same type testing but one may be, say, more heat resistant than another?

 

[ban-all-sheds]

I think there is one thing we can now say with complete certainty after 14 pages of back'n'forth:

Nobody really knows.

Therefore, when encountering a mongrel CU or DB, if you are to exhibit the highest standards of professional responsibility and duty of care you cannot do anything other than code it FI.

 

[JohnW2]

As I said, such a view would logically lead to attempts to find ways of reducing even those risks which, although theoretically possible (very little is 'impossible!), were of 'vanishingly small' probability.

Yes, that's what I've been trying to tell you.

As I said before, that could lead to ridiculous situations - like reinforcing our roofs in attempts to at least reduce the effects of impacts from very small micro-meteorites. We would all be taking anti-malarial tablets in the UK, just in case an infected mosquito manages to hitch a ride on an aircraft from an area where the disease is endemic (despite the airline's insecticide sprays!). More topically, most buildings, certainly non-domestic ones, are theoretically potentially at risk of terrorist attacks, but very few of them take any precautions to reduce that risk. ... etc. etc. etc.

Certainly in the context we are discussing, the performance of an MCB in normal operation is in no way dependent on the nature/performance any other devices.

That is wrong, and an irresponsible post to make on a public forum.

You misunderstand me, perhaps because I was not clear enough - I thought that my "in normal operation" was enough, but clearly not. What I meant is that (unlike the situation with tyres and brake pads), the satisfactory performance of an MCB is not dependent upon the presence (and nature) of other MCBs. We all know that there is at least a theoretical possibility that other devices in the vicinity could in some way adversely effect a protective device, but that's a different matter, and not 'normal operation'.

Kind Regards, John

 

[stillp]

most buildings, certainly non-domestic ones, are theoretically potentially at risk of terrorist attacks, but very few of them take any precautions to reduce that risk

That's not my experience, particularly in central London.

the satisfactory performance of an MCB is not dependent upon the presence (and nature) of other MCBs

Yes it is, of those other MCBs (and other devices) are in the immediate vicinity, as they would be in a CU.

that's a different matter, and not 'normal operation'

Wrong again.

 

[JohnW2]

I appreciate the differences mentioned but in my original point I only referred to the speed rating of the tyre, obviously all the other criteria would have to be the same.

Indeed - but, as you have admitted yourself, tyres or brake pads might exceed the minimum specification required by a Standard to differing extents, and therefore would be 'different' - perhaps to the detriment of a set of tyres or pads. Indeed, even if they all exceeded the requirements specified in the Standard by the same extent, there would probably still be scope for them to differ in respects that could adversely effect performance of a 'set of four'

Is that not analogous to MCBs which have all passed the same type testing but one may be, say, more heat resistant than another?

That would be fine if one MCB were being used in isolation (i.e. with no other devices in its proximity). In that case, if they had both passed the same testing, they would presumably be interchangeable. However, what stillp is talking about is the theoretical possibility that differing products, which had not been tested together, might conceivably influence one another to an extent which was 'of consequence'.

Kind Regards, John

 

[JohnW2]

most buildings, certainly non-domestic ones, are theoretically potentially at risk of terrorist attacks, but very few of them take any precautions to reduce that risk

That's not my experience, particularly in central London.

Hmmm. Even in central London, let alone other places, if you walk down any 'high street' I think you'd struggle to find any precautions against terrorist attacks. Whatever, even if you are going to argue about that particular example, I'm sure there is no end to the 'vanishingly small risks' that one could think of which we regard as so improbable that we do not feel that any 'action' is justified!

the satisfactory performance of an MCB is not dependent upon the presence (and nature) of other MCBs

Yes it is, of those other MCBs (and other devices) are in the immediate vicinity, as they would be in a CU.

Whether deliberately or not, you are still misunderstanding me - either that or your statement is ridiculous. You are surely not suggesting that the satisfactory performance of an MCB requires that there are other MCBs in the same enclosure?!!!!

Kind Regards, John

 

[JohnW2]

Nobody really knows. ... Therefore, when encountering a mongrel CU or DB, if you are to exhibit the highest standards of professional responsibility and duty of care you cannot do anything other than code it FI.

Fair enough. It may appease the professional conscience of an inspector by making them feel that they have "exhibited the highest standards of professional responsibility and duty of care", but it would really be a pretty meaningless gesture. As you say, "nobody really knows", and you have yourself admitted that very few people would be able or competent to undertake the required 'investigation' called for by your FI code. In other words, in practice no-one would be able to do anything about your FI code.

Kind Regards, John